The invention relates to a thermostatic valve arranged in the coolant circuit of an internal-combustion engine. Known thermostatic valves of the generic type include a main valve which is acted upon cold coolant on the one side, and by hot coolant on the other side, and is actuated as a function of temperature by way of an expansion material element. The expansion material element is coupled in a lift drive connection with the main valve via a control pin which can be moved out/in on the hot or mixing-chamber side, and on its other side is firmly supported by a capsule storing an expansion material, against an abutment in a cold (radiator-return-flow) side connection piece of the thermostatic valve. The capsule, which protrudes on the cold side when the main valve is closed, and penetrates the main valve with clearance of motion, includes an electric film resistor placed in the expansion material as the heating element. The film resistor in the capsule is supported in a heat-insulated manner with respect to the abutment acted upon by cold, and is energized in a controlled/regulated manner by way of connection lines arranged in the abutment.
A thermostatic valve of this type is disclosed in European Patent Document PCT/EP95/05053 with the International Publication Number WO96/19762. To reduce the influence of the cold water when the main valve is closed, in this thermostatic valve the capsule which stores the expansion material is activated into the supporting range on the abutment (which is acted upon cold) by the hot coolant from the mixing chamber of the thermostat. In addition, in this thermostatic valve, a precision resistor is provided in the supporting range as a heating element in thin-film construction. Furthermore, the hot-water chamber, which surrounds the expansion material element on the cold side, has an insulated construction with respect to the cold water.
The disadvantage of this thermostatic valve is the relatively high constructional expenditures which are necessary to reduce the influence of the cold water when the main valve is closed.
German Patent Document DE 295 00 897 U discloses a thermostatic valve in which the cold-water influence on the expansion material element is completely excluded by providing an electrically heatable expansion material element in the mixing chamber, through which at least the warm coolant of the internal-combustion engine flows constantly. However, this further development of the thermostatic valve with a main valve and a short-circuit valve also appears to require high expenditures with respect to construction and space.
It is an object of the present invention to provide an improved thermostatic valve of the above-mentioned type and construction, in which the cold water influence on the expansion material element is reduced significantly while the main valve is closed.
This object by the thermostatic arrangement according to the invention, in which the capsule has an end which limits the expansion material lower at the level of the main valve or on the mixing chamber side. At this end, a ring-shaped or sleeve-shaped heating element is arranged coaxially adjacent to the control pin, or individual heating elements are provided which, in an adjacent manner are distributed along the circumference of the control pin.
German Patent Document DE 1 576 699 A discloses a thermostatic valve which has a main valve that is acted upon by cold coolant in the closed condition. The expansion material element is constructed such that when the main valve is closed, it is stored essentially below this main valve and therefore exclusively on the mixing chamber side. Therefore, the cold water influence is significantly reduced. However, this expansion material element shows no electric heating device.
German Patent Document DE 1 476 445 A describes a thermostatic valve which has an expansion material element in which the level of the expansion material in the expansion material capsule on the mixing chamber side is arranged particularly low with respect to the main valve.
Finally, in European Patent Document EP 0 838 580 A, a thermostatic valve with a main valve acted upon on the cold side has an electric heating element provided in the expansion n material element, away from the side acted upon cold, in the mixing chamber area. While the electric output of the heating element is the same, by means of this arrangement faster and more precise regulation is possible. However, this embodiment has the disadvantage that the connection lines for feeding the electric energy through the hot coolant are guided to the movable end of the expansion material element supported on the cold side. A high-expenditure running of cables is therefore absolutely necessary to avoid cable breaks.
Thus the combination according to the invention of an expansion material level which is relatively low on the mixing chamber side in the capsule, in conjunction with a heating element closely adjacent to the control pin in the area of the mixing chamber, represents an advantageous combination for a further development of the thermostatic valve of the above-mentioned type which has a simpler construction.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.